U.S. Pat. No. 3,083,698 and 3,158,930 disclose brake boosters having a housing manufactured in a well known method wherein an end surface on a first shell is crimped by cutting or shearing tabs that engage a surface on a second shell to define a unitary structure. Such crimped joints function in an adequate manner to seal the interior of the unitary structure for use as a housing for a brake booster. When used for a brake booster it was a common practice to spray paint the exterior surface of the shells to protect against oxidation of the shells that are exposed to the environment when installed in a vehicle. Unfortunately, the painting process while effective often did not provided a uniform protection over the entire exterior surface of a shell and as a result some oxidation could occur after a period of time. In an effort to better protect the shells, a process known as e-coating was developed which uniformly coats the shell and this process is now an accepted standard for protection with respect to oxidation. However, in the crimping process of joining the first shell to the second shell certain portions of the first shell are either sheared or stretched such that the sheared portion of the first shell has bare metal exposed to the environment and over a period of time this bare metal oxidizes and creates an undesirable appearance for the brake booster. While it would be possible to re-coat or touch up the bare or exposed metal after crimping, the time, effort and labor involved would add considerable cost to the manufacturing process which a customer would be hesitant to absorb as no tangible functional benefit of the brake booster would occur from such added effort.
A primary object of the present invention is to provide a housing for a brake booster wherein the entire external surface has a coating that remains after a crimping or deformation process used to join a first shell to a second shell to define a sealed unitary structure.
According to this invention, a housing for a brake booster is manufactured by deforming a first peripheral surface on a coated first shell around a second peripheral surface on a coated second shell toward an axial center of the second shell. The deformation axially compresses a bead on a diaphragm located between the first and second shells to seal an interior of the housing from the surrounding environment. The first shell is characterized by a cylindrical body with a closed end and an opened end. The cylindrical body has a first peripheral surface with a flange that extends from a shoulder to an opened end. The flange has a plurality of slits axially that extend from the opened end toward the shoulder to define a plurality of spans adjacent the opened end. A plurality of slots are located in flange in a radial plane perpendicular to the opened end and sequentially adjacent a mid-point of the plurality of spans. Each of the slots has a first and second semi-circular relief that extends into a span and toward the opened end of the first shell. A deformation of the first peripheral surface occurs by either rolling the spans into engagement with the second peripheral surface to position the second peripheral surface with respect to the shoulder such that the second peripheral surface is aligned in the plurality of slots or a first force is applied to compress the second shell toward the first shell such that the second peripheral surface is aligned in the plurality of slots and a second force is applied at each a mid-point between the first and second semi-circular reliefs to dent the span into engagement with the second peripheral surface and retain the compressive force on the bead to join the first shell with the second shell such that the flange retains a circular shape without any un-coated peripheral areas exposed to the environment.
An advantage of this invention resides in a method of joining a first shell to a second shell without the exposure of any un-coated surfaces which could oxidize over a period of time in an oxygen rich environment.
A still further advantage of this invention resides in a unitary structure wherein a first shell has a flange with a plurality of slits and slots define a controlled plane whereby deformation is achieved to retain a second peripheral surface in a fixed relationship with a first peripheral surface to create a sealed housing.
Another advantage this invention resides in a visual inspection of a connection between a first shell and a second shell to assure that a sealed relationship is achieved.
A still further advantage of the present invention resides in a method of manufacturing a housing for a brake booster wherein deformation of a flange occurs without exposing bare metal to the environment.